The covalent modification of sulfhydryl groups by S-nitrosoglutathione has been examined using model compounds. S-Nitrosoglutathione and thiol compounds causing extremely fast transnitrosation reaction and subsequent production of mixed disulfide. Yeast alcohol dehydrogenase is rapidly inactivated by S-nitrosoglutathione. The reversibility and Ellman test demonstrate that the inactivation is the result of covalent modification of sulfhydryl groups in this enzyme.